题解 | #反转链表#

空间O（2）

/*
public class ListNode {
    int val;
    ListNode next = null;

    ListNode(int val) {
        this.val = val;
    }
}*/
public class Solution {
    public ListNode ReverseList(ListNode head) {
        ListNode next,nextp;
        if(head == null){
            return null;
        }
        if(head.next == null){
            return head;
        }
        next = head.next;
        nextp = next.next;
        head.next = null;
        while(nextp != null){
            next.next = head;
            head = next;
            next = nextp;
            nextp = nextp.next;
            
        }
        next.next = head;
        return next;
    }
}